Patent GB-1052942-A (GB)
IPC: G05B19/04
Abstract: 1,052,942. Machine tools. H. B. F. JENSEN. Dec. 3, 1962 [Dec. 27, 1961], No. 46270/61. Headings B3B and B3C. [Also in Divisions H3 and G3] In a sequential control system e.g. for a machine tool, a binary counter is stepped by signals provided by a plurality of sensing devices (e.g. switches) each sensitive to the completion of an operation, outputs from the binary counter are distributed by a binary/ decimal converter to a plurality of lines each controlling an operation and each line also being connected to the sensing devices so as to permit a further stepping signal when the appropriate device is actuated. Automatic control of drilling machines.- Fig. 1 shows a drilling machine in which the completion of each operation is indicated by the closing of a sensing switch U2 ... U8 which, as will be described, results in the initiation of the next operation. An hydraulic or pneumatic cylinder H2 moves the lower workpiece from a magazine 102 into a drilling position where it is clamped by a pressure shoe under control of a cylinder H1. The vertical feed of the drill is controlled by a third cylinder H3. The finished workpiece is ejected when the slide 110 positions the next workpiece, the ejected workpiece interrupting a beam of light emitted from a source 96 on to a photo-sensitive element 97. Fig. 4 shows a block diagram of a control system for such a machine. A sequence of operations is started by closing switch U1 thus feeding signals along line y to an input network INP of a binary counter comprising four transistorized bistable circuits BN1 ... BN4. Outputs from the counter are fed to transistorized gates DP1 ... DP11 in such a way as to open a particular gate at each step of the counter. An output from each gate is distributed via a plug board M2 to one or more bi-stable circuits RA ... RC, which energize relays RV, controlling solenoids H1 ... H3 which in turn actuate pneumatic or hydraulic cylinders to perform the required operation. The output of each gate is also fed via isolating diodes to the sensing switches U1 ... U10 so that a further signal is produced on line y when the appropriate switch is closed at the completion of the next operation. Bi-stable relay-operating circuit RA (Fig. 4).- Each circuit RA ... RC is energized by signal at I1 which turns off transistor RT2 and turns on transistor RT3, energizing relay RV, the contacts of which energize the solenoid-controlled cylinder. Relay RV remains energized until a signal is received at I2 when transistor RT1 is turned off, turning on RT2 and turning off RT3, thus releasing relay RV. Capacitors C<SP>1</SP>2, C<SP>1</SP>3 by-pass spurious signals; C<SP>1</SP>1 bypasses the inductive surge from relay RV. Triggering binary counting stages (Fig. 5).- Each time one of the sensing switches U1 ... U10 is closed a positive signal is fed along line y to turn on diode D1 and turn off diode D2 so that the rise in potential at point C turns off transistor TF2, turning on TF3, thus feeding a positive signal to the bi-stable circuit BN1. The positive step from TF3 turns off TF4 which turns on TF1. The circuit is reset after a time determined by the discharge of capacitor C1 via resistor r4 and TF1. Each signal on line 1 is thus converted into a positive-going pulse of predetermined duration. Each pulse from the INP unit is steered via diodes V, V<SP>1</SP> to the conductive transistor TB1 or TB2 of the first binary stage BN1, reversing the conductive state of transistors TB1, TB2 once per pulse. The output from BN1 is fed to the other binary stages BN2 ... BN4. Transistor AND gates DP (Fig. 5).-Transistor TD1 is turned off when the appropriate output from each binary stage is positive. The negative voltage at the collector thus turns on transistor TD2 which connects line f to the appropriate sensing switch U1 ... U10. Emergency stopping and safety precautions (Fig. 5).-When the starting switches SS1, SS2 are closed, transistor FT1 becomes conductive, energizing relay RF which remains energized via a holding contact k2. Contacts k1 feed a control voltage to line f. Resistors rt12, rt13 are adjusted so that when, under normal operation, only one of lines u1 ... u10 is connected to line f at any time, the voltage across rt12 is just sufficient to keep transistor FT6 non-conductive. If, under fault conditions, more than one line u1 ... u10 becomes connected to line f, FT6 becomes conductive, reversing the conductive states of the bi-stable pair of transistors FT2, FT3 so that transistor FT1 is turned off, releasing relay RF and interrupting the control voltage from line f. A similar result will be caused by the action of line m1 if more than one switch U1 ... U10 remains closed. If the emergency switch ES is opened relay RF will be similarly released. A line b is provided to block the INP unit so as to prevent spurious stepping of the binary counting chain if relay RF is released. Contacts SS2 of the starting switch ensure that the bi-stable circuit FT2, FT3 is in the required conductive state when commencing operation. Resetting (Fig. 5).-The conductive state of bi-stable transistors FT4, FT5 is reversed by the charging of capacitor Ct3 when the supply to unit RFB is first connected, the change in collector voltage of FT5 is fed along the line z to reset all the binary stages. The reset signal is terminated by reversing the conductive state of FT4, FT5 when the contacts SS2 of the starting switch are closed. Systems using more than one counter.-Figs. 6, 8, 9 (not shown) relate to arrangements comprising two counting circuits of the type shown in Fig. 5. Binary stages (BN1 ... BN4) are stepped by sequential operation of sensing switches u1 ... u15 which feed signals via an electronic switch (Me0<SP>-</SP>) (see Division H3) and input circuit INP. When switch u15 is closed. a pulse reverses the connections of electronic switch (Me0) so that binary stages (BN1 ... BN4) are now controlled by sequential closing of further sensing switches u16 ... u30.